XBAR Resonator With Uniform Dielectric Overlayer for High-Band RF Filtering
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those proposed for future wireless networks, which require improved performance and frequency separation capabilities.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with specific design features, including thin film conductors and a unique pitch and width configuration for the IDT fingers, to achieve high piezoelectric coupling and efficient frequency separation, enabling the design of filters suitable for frequencies above 3 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used, then the filter structure is simple and easy to manufacture, but the frequency separation capability and performance are insufficient for higher frequency communications bands
Solution Approach 1:
The patent changes the geometric parameters of the IDT fingers, specifically using a pitch-to-width ratio (p/w) of 2:1, which is significantly different from conventional designs. This parameter change enables enhanced frequency separation capability and improved performance at higher frequency bands while maintaining manufacturing feasibility
Solution Approach 2:
The patent employs a composite structure combining piezoelectric material layers with specific dielectric materials. The piezoelectric layer is configured with particular thickness ratios relative to the acoustic wavelength, creating a composite resonator structure that achieves superior frequency separation and high-frequency performance
2Use of energy by moving object
If the IDT finger pitch and width are increased to improve coupling, then the piezoelectric coupling is enhanced, but the frequency separation capability deteriorates
Solution Approach 1:
The patent optimizes the IDT finger dimensions by setting the pitch-to-width ratio to 2:1 and configuring the piezoelectric layer thickness to be between 0.2λ and 0.5λ (where λ is the acoustic wavelength). This specific parameter configuration achieves a balance that provides both strong piezoelectric coupling and effective frequency separation
Solution Approach 2:
The patent applies different material properties and geometric configurations to different regions of the resonator. The piezoelectric layer has specific thickness variations and material characteristics that are optimized locally to enhance coupling in certain areas while maintaining frequency separation in others
3Manufacturing precision
If a uniform-thickness dielectric overlayer is applied, then the manufacturing precision and fabrication simplicity are improved, but the frequency tuning capability is reduced
Solution Approach 1:
The patent configures the dielectric overlayer with a uniform thickness of between 0.1λ and 0.3λ, which provides manufacturing simplicity and precision while the specific thickness range maintains adequate frequency tuning capability through the piezoelectric coupling mechanism
Solution Approach 2:
The uniform-thickness dielectric overlayer serves multiple functions simultaneously: it provides mechanical support, electrical insulation, and contributes to the overall resonator frequency characteristics. This multi-functionality reduces the need for additional tuning layers while maintaining performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
XBARs provide enhanced performance and bandwidth capabilities, allowing for the effective filtering of higher frequency communications bands, including millimeter wave frequencies, with improved rejection and insertion loss characteristics.
Implementation Method 1
an interdigital transducer (IDT) configured on the piezoelectric substrate, wherein the IDT comprises a first set of IDT fingers and a second set of IDT fingers that are interleaved with the first set of IDT fingers
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) with specific design features
Data Source
AI summary
Acoustic filters, resonators and methods are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces and a thickness ts, the back surface attached to the surface of the substrate except for portions of the piezoelectric plate forming a plurality of diaphragms that span respective cavities in the substrate. A conductor pattern is formed on the front surface of the piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a plurality of acoustic resonators, interleaved fingers of each IDT of the plurality of IDTs disposed on a respective diaphragm of the plurality of diaphragms. Zero or more dielectric layers are deposited over all of the IDTs and the diaphragms, wherein a total thickness of the zero or more dielectric layers is the same for all of the plurality of acoustic resonators.